CN115717643A

CN115717643A - Hydromechanical transmission and control method

Info

Publication number: CN115717643A
Application number: CN202211023797.8A
Authority: CN
Inventors: G·普罗夫莫; L·达拉帕尔马
Original assignee: Dana Italia SRL
Current assignee: Dana Italia SRL
Priority date: 2021-08-24
Filing date: 2022-08-24
Publication date: 2023-02-28
Also published as: DE102022208703A1

Abstract

The invention relates to a method and a system for a hydromechanical transmission. In one example, the transmission system includes a hydraulic pump and a hydraulic motor rotationally coupled in parallel with the first and second planetary gear sets. In this system, a sun gear of the planetary gear set is rotationally coupled to the hydraulic motor, a carrier of the first planetary gear set is rotationally coupled to the first clutch and the second clutch, and a ring gear of the second planetary gear set is rotationally coupled to the third clutch.

Description

Hydromechanical transmission and control method

Technical Field

The present disclosure relates to a hydromechanical transmission and a method for adjusting the drive range of the transmission.

Background

Hydromechanical transmissions are capable of blending the performance characteristics (e.g., efficiency, shift quality, drive characteristics, control response, etc.) of both mechanical and hydrostatic transmissions to meet certain design goals. Some hydro-mechanical transmissions, referred to in the art as hydro-mechanical variable transmissions (HVTs), provide continuously variable gear ratios. Hydromechanical transmissions may be particularly desirable due to their efficiency and Power Take Off (PTO) capabilities. Vehicles for industries such as agriculture, construction, mining, materials handling, oil and gas, etc. therefore use HVT.

U.S. Pat. No. 7,530,914 B2 to Fabry et al teaches a hydromechanical transmission having two synchronizers and two clutches. The synchronizing device and the clutches work in concert to shift the transmission between the high and low speed ranges in forward and reverse modes of operation. In US 7,530,914 B2, each clutch is paired with a synchronizer on a common shaft. Further, due to packaging constraints imposed by the transmission components, each pair of clutches and synchronizers are spaced apart from one another.

The inventors have recognized several shortcomings of the Fabry transmission as well as other hydro-mechanical transmissions. For example, the synchronizer of the Fabry may be susceptible to degradation, which generally reduces transmission reliability. Furthermore, the synchronization device adds to the system cost and complexity. Other hydromechanical transmissions make unnecessary compromises in transmission complexity, packaging efficiency, operating drive range, and smoothness of shifting.

To address at least a portion of the above problems, the inventors have developed a transmission system. The transmission system includes a hydraulic pump and a motor. The hydraulic motor is rotationally coupled in parallel with the first and second planetary gear sets. In the system, sun gears of the first and second planetary gear sets are rotationally coupled to a hydraulic motor. Further, in the system, the carrier of the first planetary gear set may be rotationally coupled to the first clutch and the second clutch. Additionally, the ring gear of the second planetary gear set may be rotationally coupled to the third clutch. Providing a transmission with a sun gear and clutch of this layout allows the system to achieve a compact design and a target number of available drive ranges.

Further, in one example, the first clutch may be a first forward drive clutch and the second clutch may be a reverse drive clutch disposed adjacent and coaxial with the first forward drive clutch. Positioning the clutches in this manner increases transmission space efficiency while allowing the system to achieve the first forward drive range and the reverse drive range.

In another example, a transmission system may include a mechanical PTO and an input shaft that receives rotational input from a prime mover power source. Providing a mechanical PTO further increases the flexibility of the system and allows the system to be used in a wider range of vehicle applications, if so desired.

It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.

Drawings

FIG. 1 is a schematic illustration of a vehicle having a hydromechanical transmission.

FIG. 2 is a first example of a hydromechanical transmission system.

3-8 are diagrammatic views of the hydromechanical transmission system depicted in FIG. 2 operating under different conditions within the system drive range.

Fig. 9 is a diagram showing the configuration of the clutch for different drive ranges.

FIG. 10 is an exemplary graphical representation of hydrostatic pressure ratio versus gear ratio over different drive ranges.

11-12 are exemplary illustrations of pump rotation angles versus hydrostatic pressure ratios in a hydrostatic assembly.

FIG. 13 is a method for operating a transmission system to shift between drive ranges.

FIG. 14 is an exemplary illustration of a transmission power limit curve.

FIG. 15 shows an exemplary plot of transmission speed versus time and transmission tractive torque versus time.

FIG. 16 shows an exemplary plot of clutch differential speed versus time and clutch pressure versus time.

Fig. 17 shows an exemplary plot of hydrostatic motor torque versus time and clutch pressure versus time.

Fig. 18 shows an example of reverse gear operation in the transmission shown in fig. 1.

Detailed Description

A hydromechanical transmission and a method for operating the transmission are provided herein. Hydromechanical transmissions enable synchronous shifting in a space-saving package. The transmission includes one reverse clutch and two forward clutches coupled in parallel with each other and first and second planetary gear sets to achieve a desired ganged operating drive range. In one example, one of the reverse clutch and the forward drive clutch may be rotationally coupled to a common shaft. This dual clutch design can reduce manufacturing costs and enable a more compact design of the transmission. Further, in such an example, the second forward drive clutch may rotate on an axis offset from the other clutches and the planetary assembly. In this way, the transmission may achieve a target degree of descent (e.g., distance between the input and output interfaces). Further, in one example, the hydrostatic assembly in the transmission may be a U-shaped hydrostatic unit with mechanical input shafts for a hydraulic pump (e.g., a variable displacement pump) and a motor (e.g., a fixed bent-axis motor) parallel to each other and arranged on one side of the unit. This allows for a reduction in the size of the unit and avoids the use of high pressure hoses to reduce manufacturing costs and the chance of deterioration of the hydrostatic unit.

In a transmission, a hydrostatic branch including a hydraulic motor and a pump is arranged in parallel with a mechanical branch and coupled to a motive power source (e.g., an engine, an electric motor, a combination thereof, or other suitable prime mover). In one example, the sun gears of the planetary gear sets are rotationally coupled to each other and to the hydrostatic branch. Because the sun gears are attached together, the transmission can achieve greater space efficiency.

The shift strategy employed in the system may include maintaining one of the clutches open while simultaneously opening and closing the remaining clutches. Such a shift strategy may be used to smoothly transition between two drive ranges in a set of drive ranges including a reverse drive range and two forward drive ranges. Thus, power outages and noise, vibration, and harshness (NVH) during shift transients may be reduced (e.g., avoided). Furthermore, when such a shifting strategy is used, the efficiency of the transmission may be improved.

FIG. 1 shows a schematic diagram of a transmission system with hydromechanical power splitting. Fig. 2 shows a first example of a transmission system designed to provide continuously variable input-to-output speed adjustability using wolf symbol scheme (wolf symbol scheme). 3-8 depict a first example of a transmission system in different operating drive ranges, where power is additively combined or recirculated using a power splitting arrangement. FIG. 9 shows a chart representing states of clutches in a first example of a transmission system in different drive ranges. FIG. 10 shows an exemplary graph of hydrostatic pressure ratio versus mechanical gear ratio over different drive ranges. 11-12 depict example graphs of pump rotation angle versus hydrostatic pressure for forward and reverse drive ranges. The examples used herein do not give any kind of precedence indication but represent one of a variety of potential configurations. FIG. 13 illustrates a method for smoothly and efficiently shifting between drive ranges in a transmission system. As described herein, smooth shifting refers to reducing (e.g., avoiding) shift events in which power is interrupted. Thus, smooth shifting may significantly reduce or, in some cases, avoid power transfer spikes or dips during the shifting operation. Thus, smooth shifting allows for improved transmission efficiency as well as drivability and driving comfort of the vehicle. FIG. 14 depicts an example power limiting curve for a hydromechanical transmission. 15-17 depict different graphical representations with curves embodying a use case shift strategy. FIG. 18 illustrates the transmission of FIG. 1 during a reverse shift operation.

Fig. 1 shows a schematic diagram of a transmission system 100 (e.g., a hydromechanical variable transmission) in a vehicle 102 or other suitable machine platform. In one example, the vehicle may be an off-highway vehicle, although in other examples the transmission may be deployed in an on-highway vehicle. An off-highway vehicle may be a vehicle whose size and/or maximum speed is such that the vehicle cannot operate on a highway for extended periods of time. For example, the width of the vehicle may be greater than the roadway lanes, and/or the vehicle top speed may be lower than the lowest allowable or recommended speed for the roadway, for example. Industries in which vehicles may be deployed and their corresponding operating environments include forestry, mining, agriculture, and the like. In either case, the vehicle may be designed with an auxiliary system driven via a hydraulic and/or mechanical power take-off (PTO).

The transmission system 100 may be used as an Infinitely Variable Transmission (IVT) in which the gear ratio of the transmission is continuously controlled from negative maximum speed to positive maximum speed in an infinite number of ratio points. In this way, the transmission can achieve a relatively high level of flexibility and efficiency with respect to transmissions operating in discrete ratios. Further, in one example use, the transmission may be configured to operate in an ambient temperature range of-40 ℃ to 80 ℃. In such an example, the sump in the gearbox lubrication system may operate in a range between-40 ℃ and 100 ℃. However, the transmission may be designed for various operating temperature ranges. Further, in some examples, the transmission system may be designed to operate on a longitudinal grade of up to 35 degrees and a lateral grade of 25 degrees. The longitudinal grade and/or lateral grade thresholds may be adjusted (e.g., increased or decreased) to accommodate different end-use design goals.

The transmission system 100 may have asymmetric maximum output speeds for forward and reverse directions (e.g., reverse drive speed may provide approximately 56% forward drive speed). This forward-reverse speed asymmetry may enable the transmission to achieve a desired width of speed range. However, other suitable output speed variations have been contemplated, such as symmetrical output speeds in the forward and reverse directions, however, this may require the use of additional clutches which may increase system complexity.

The transmission system 100 may include a motive power source 104 or receive power from the motive power source 104. The power source 104 may include an internal combustion engine, an electric motor (e.g., a motor-generator), combinations thereof, and the like. In one use case example, the power source 104 may generate greater than 80 kilowatts (kW) (e.g., 100-115 kW). In detail, in some cases, the power source may operate in a range between 900-2100 Revolutions Per Minute (RPM), with a target range between 1200-1600 RPM. Further, in some examples, engine idle speed may be approximately 650RPM. However, many suitable transmission operating and idle ranges have been contemplated.

A torsional damper coupling 106 may further be provided in the transmission.

Gears

108, 110, such as bevel gears, may be used to rotationally couple power source 104 to input shaft 112. As described herein, a gear may be a mechanical component that rotates and includes teeth that are contoured to mesh with teeth in one or more corresponding gears to form a mechanical connection that allows rotational energy to be transmitted therethrough.

A mechanical PTO 114 may be coupled to the input shaft 112. The mechanical PTO 114 may drive auxiliary systems such as pumps (e.g., hydraulic pumps, pneumatic pumps, etc.), winches, booms, bed lifting assemblies, and the like. To accomplish the power transfer to the auxiliary components, the PTO may include an interface, one or more shafts, a housing, and the like. However, in other examples, the PTO may be omitted from the transmission system. The gear 116 may be coupled to the input shaft 112. The mechanical assembly 118 may also be included in the transmission system 100. The mechanical assembly 118 may include the shaft 112 and/or the gear 116 and a shaft 167, described in more detail herein. Further, the transmission may include a shaft 120 and a gear 122, the gear 122 being rotationally coupled to the gear 116 on the input shaft 112. The dashed line 124 depicted in fig. 1 and the other dashed lines indicate mechanical connections between the components that facilitate rotational energy transfer therebetween.

A gear 126, which meshes with the gear 122, is rotatably attached to the charge pump 128. The charge pump 128 may be designed to deliver pressurized fluid to hydraulic components in the transmission, such as a hydraulic motor 134 (e.g., hydrostatic motor), a hydraulic pump 136 (e.g., hydrostatic pump), and so on. The fluid pressurized by the charge pump may additionally be used for clutch actuation and/or transmission lubrication. The charge pump may include a piston, rotor, housing, one or more chambers, etc. to allow the pump to move fluid. In parallel, the mechanical assemblies 118 are rotationally coupled to a hydrostatic assembly 130 (e.g., a hydrostatic unit). Furthermore, hydrostatic assembly 130 may have a U-shaped design, with

shafts

131, 133 serving as mechanical interfaces for a hydraulic pump 136 (e.g., a variable displacement pump) and a hydraulic motor 134 (e.g., a fixed bent axis motor), respectively, and in parallel with each other and arranged on one side of the assembly. This U-shaped layout allows for a reduction in the size of the hydrostatic assembly and can enable the use of high pressure hoses to be eliminated, reducing manufacturing costs and the likelihood of deterioration of the hydrostatic unit, if desired. Still further, the hydrostatic assembly 130 may be disposed on an opposite side of the transmission from the charge pump 128 and/or axially offset from the

clutches

170, 172. Arranging the hydrostatic assemblies in this manner allows the width and length of the transmission to be reduced and allows the installation of the transmission in a vehicle to be simplified. Further, the motor and pump in the hydrostatic assembly may be enclosed in a common housing to increase transmission compactness.

The coupling of the hydrostatic assembly with the mechanical assembly enables the transmission to implement a power split functionality, wherein power may flow through either path synchronously to additively combine or recirculate power through the system. This power splitting arrangement enables the power flow of the transmission to be highly adaptable for increased efficiency over a wide range of operating conditions. Thus, in one example, the transmission may be a full power split transmission.

Mechanical assembly 118 may include multiple mechanical paths coupled in parallel to a hydrostatic assembly. In detail, the shaft 167 may serve as a junction of the first mechanical path (e.g., branch) 119 and the second mechanical path (e.g., branch) 121. The first mechanical path 119 may provide a rotational energy transfer capability from the interface of the hydrostatic assembly 130 to the ring gear 158 of the first planetary gearset 148 during certain operating conditions. Further, the second mechanical path 121 may provide rotational energy transfer capability from the interface of the hydrostatic assembly 130 to the planet carrier 160 of the second planetary gear set 150.

Hydrostatic assembly 130 includes a hydraulic motor 134 and a hydraulic pump 136. Further, the hydraulic pump 136 may include a first mechanical interface 138 and a second mechanical interface 140. First mechanical interface 138 is rotatably coupled to mechanical bushing 132, while second mechanical interface 140 is rotatably coupled to another mechanical PTO 142. Likewise, mechanical PTOs may be used to drive auxiliary vehicle systems such as air compressors, robotic arms or booms, augers, and the like. In this way, the transmission may be adapted for various end use operating environments. If desired, multiple PTOs are provided in the arrangement depicted in FIG. 1, enabling the transmission system to meet end use design goals for a variety of different types of vehicles. Thus, the applicability of the system is expanded, and the customer appeal of the transmission is increased. However, in other examples, PTO 114 and/or 142 may be omitted from the transmission.

In one example, the hydraulic pump 136 may be a variable displacement bi-directional pump. Additionally, in one instance, the pump may be an axial piston pump. In detail, in one particular example, an axial piston pump may include a tilted plate that interacts with the pistons and cylinders to vary the displacement of the pump via changes in the angle of rotation. However, other suitable types of variable displacement bidirectional pumps have been contemplated.

The hydraulic motor 134 may be a fixed displacement bi-directional motor (e.g., a fixed bent axis motor). Fixed bent-axis motors are relatively compact when compared to variable displacement motors. The system may thus achieve greater space efficiency and impose fewer space constraints on other systems in the vehicle, if desired. However, alternative types of pumps and/or motors may be used, for example, if motor adjustability comes at the expense of compactness.

Hydraulic lines

144, 146 are attached to hydraulic interfaces in each motor and pump to enable the hydrostatic assembly to provide additional and power cycling functionality with respect to mechanical branches arranged in parallel with the hydrostatic assembly 130. For example, in the additional power mode, power from both the hydrostatic and mechanical components is combined at one of the planetary gear sets and delivered to the transmission output. Thus, the hydraulic pump 136 and the hydraulic motor 134 may be operated to flow power from the hydraulic motor to the sun gear of any planetary assembly. In the recirculation power mode, power is recirculated through the hydrostatic assembly. Thus, in the recirculation power mode, power flows from the hydrostatic assembly to the shaft 120.

The transmission system 100 also includes a first planetary gear set 148 and a second planetary gear set 150. The first planetary gear set 148 may include a planet carrier 152 on which planet gears 154 rotate. The planet gears 154 may mesh with a sun gear 156 and a ring gear 158. Likewise, the second planetary gear set 150 may include a planet carrier 160, planet gears 162, a sun gear 164, and a ring gear 166. Thus, the second planetary gear set 150 may also be a simple planetary gear. Furthermore, a bearing arranged between the planet gear and the planet carrier in each planetary arrangement may facilitate its rotation. The sun gears and/or the shafts to which they are attached may also have bearings coupled thereto. The bearings may be roller bearings (e.g., needle bearings), ball bearings, or other suitable types of bearings that enable the components to rotate while limiting other relative movement.

The carrier 160 of the second planetary gear set 150 is rotatably coupled to the ring gear 158 of the first planetary gear set 148. Furthermore, the carrier 160 of the second planetary gear set 150 is rotatably coupled to a shaft 167. The shaft 167 may extend through a central opening in the extension 186, described in more detail herein. This rotational attachment scheme may be conceptually described as the formation of mechanical branches attached in parallel to hydrostatic assembly 130.

As described herein, parallel attachment between components, assemblies, etc. means that the inputs and outputs of two components or groups of components are rotationally coupled to each other. This parallel arrangement allows power to be recirculated through the hydrostatic assembly during certain conditions, or to be additionally combined by the mechanical and hydrostatic branches during other conditions. Thus, the transmission has improved adaptability compared to a purely hydrostatic transmission, which allows a gain in operating efficiency to be achieved.

The sun gears 156, 164 of the first and second planetary gear sets 148, 150 may be rotationally coupled to each other (e.g., directly attached). Attaching the sun gear in this manner may enable the transmission to achieve desired gear ratios, compactness, and efficiency.

For example, the hydraulic motor 134 may be rotationally coupled to the sun gear 156 via a mechanical bushing 168. The transmission system 100 further includes a reverse clutch 170, a first forward drive clutch 172, and a second forward drive clutch 174. More generally, the first forward drive clutch may be referred to as a first clutch or a first forward clutch, the reverse drive clutch may be referred to as a second clutch or a reverse clutch, and the second forward drive clutch may be referred to as a third clutch or a second forward clutch.

Clutches

170, 172, 174 may be positioned proximate output shaft 171 and downstream of the planetary assembly. Placing the clutch in this position allows a desired compromise between clutch size and clutch speed. For example, relatively high clutch speeds may result in high power losses. Further, the reverse clutch 170 and the first forward drive clutch 172 may be disposed adjacent to each other and coaxial with each other. In one particular example, the clutch may be of similar design to reduce manufacturing complexity. This double clutch arrangement therefore allows a reduction in manufacturing costs and an increase in the compactness of the transmission.

The

clutches

170, 172, 174 may be friction clutches, each clutch including two sets of plates. The clutch plates are rotatable about a common axis and are designed to engage and disengage one another to facilitate selective power transfer to downstream components. In this way, the clutches can be closed and opened to place them in engaged and disengaged states. In the disengaged state, power does not pass through the clutch. In contrast, in the engaged state, power travels through the clutch during operation of the transmission. Further, the clutch may be hydraulically, electromagnetically and/or pneumatically actuated. For example, the clutch may be adjusted via a hydraulic piston. The adjustability may be continuous, in one example, where the clutch may transition through a partially engaged state to a fully engaged state, where relatively little power loss occurs in the clutch. However, in other examples, the clutch may be adjusted discretely.

The planet carrier 152 may include an extension 175 having a gear 176, the gear 176 being in mesh with a gear 177. In the illustrated example, the gear 177 is rotationally coupled to the reverse clutch 170 and the first forward clutch 172. The reverse clutch 170 and the first forward clutch 172 are shown disposed adjacent to one another and may share a common axis of rotation. Due to this close clutch arrangement, the system may exhibit greater compactness, resulting in less space constraints on adjacent vehicle systems. Alternatively, the reverse clutch may be spaced from the first forward clutch, but this may reduce the compactness of the system.

Gear 179 may be located on an output shaft 180 of the reverse clutch 170. Similarly, a gear 181 may be located on the output shaft 182 of the first forward clutch 172. Both gears 179, 181 may be rotationally attached to the system output shaft 171 via

gears

183, 184, respectively. In this way, both the reverse clutch and the first forward clutch deliver power to the output of the transmission during different operating conditions.

The system output shaft 171 may include one or more interfaces 185 (e.g., yokes, gears, chains, combinations thereof, and the like). The output shaft is specifically shown as having two outputs. However, the transmission may include an alternate number of outputs. Gear 179 is rotationally coupled to the output shaft via meshing with gear 183. Arrow 191 depicts the flow of power from the transmission system to the transaxle 192 and/or other suitable downstream vehicle components, and vice versa. A transmission system having shafts, joints, etc. may be used to perform power transfer between the transmission and the shafts. It should be understood that the drive axle may be coupled to a drive wheel.

The ring gear 166 of the second planetary gear set 150 may include an extension 186 on which a gear 187 is positioned. As shown in phantom, gear 187 is rotatably attached to gear 188 in the second forward clutch 174. Gear 188 may be coupled to a first set of plates in clutch 174. A second set of plates in the clutch may be attached to the output shaft 189 and gear 190. Gear 190 is rotatably coupled to gear 183 as shown by the dashed lines. Due to the foregoing arrangement of the clutches and planetary gear sets, the transmission system 100 achieves higher efficiency and enhanced drivability, comfort and productivity than previous hydromechanical transmissions.

The transmission system 100 may additionally include a lubrication system, which may include a sump, as previously described. The lubrication system may also include conventional components for lubricating gears and/or clutches, such as pumps, conduits, valves, and the like.

A control system 193 having a controller 194 may further be incorporated into the transmission system 100. Controller 194 includes a processor 195 and a memory 196. Memory 196 may hold instructions stored therein that, when executed by a processor, cause controller 194 to perform the various methods, control strategies, and the like described herein. Processor 195 may include a microprocessor unit and/or other types of circuitry. Memory 196 may comprise known data storage media such as random access memory, read only memory, keep alive (keep alive) memory, combinations thereof, and the like.

The controller 194 may receive vehicle data and various signals from sensors positioned in different locations of the transmission system 100 and/or the vehicle 102. The sensors may include

gear speed sensors

197, 198, 199 that detect the speed of gear 116, gear 184, and gear 176, respectively. In this way, the gear speeds at the input and output of the system may be detected along with the gear speed at the output of the first planetary gear set 148. However, in other examples, the speed of at least a portion of the gears may be modeled by the controller.

Controller 194 may send control signals to actuators in hydraulic pump 136 or an actuation system coupled to the pump to adjust the pump output and/or the direction of hydraulic fluid flow. Additionally, the

clutches

170, 172, 174 may receive commands (e.g., open or close commands) from a controller, and the clutches or an actuator in an actuation system coupled to the clutches may adjust the state of the clutches in response to the received commands. For example, the clutch may be actuated via a hydraulically controlled piston, although other suitable clutch actuators have been contemplated. Other controllable components in the transmission system include hydraulic motor 134, motive power source 104, and the like. These controllable components may similarly function in connection with receiving control commands and adjusting the output and/or state of the assembly in response to receiving commands via the actuator. Additionally or alternatively, a vehicle Electronic Control Unit (ECU) may be provided in the vehicle to control the power sources (e.g., the engine and/or the motor). In addition, the control system 193, and in particular the controller 194 having the memory 196 and the processor 195, may be configured to execute the gear shifting methods detailed herein with respect to fig. 3-8 and 13.

The transmission system 100 may include an input device 151 (e.g., an accelerator pedal, a lever, a joystick, a button, combinations thereof, or the like). In response to driver inputs, the input device 151 may generate a transmission speed or torque adjustment request and a desired drive direction (forward or reverse). Further, the transmission system may automatically shift between drive modes when needed. In particular, an operator may request a change in speed or torque for forward or reverse drive modes, and the transmission may increase the speed or torque and automatically transition between drive ranges associated with the different drive modes, if desired. Further, in one example, the operator may request reverse drive operation while the vehicle is operating in a forward drive mode. In such an example, the transmission may automatically initiate a shift between forward and reverse drive modes (e.g., a synchronous shift). In this way, the operator may more effectively control the vehicle than a transmission designed for manual driving mode adjustment. However, in other examples, the system may be designed to allow a vehicle operator to manually request a mode change between forward drive ranges, for example. It should also be appreciated that the power source may be controlled in coordination with the transmission. For example, when the controller receives a requested speed adjustment, the output speed of the power source may be increased accordingly.

FIG. 2 shows a diagrammatic view of a transmission system 200 that uses a wolf symbol scheme. In the wolf-shaped version, the lines represent shafts, gears and/or other mechanisms for rotational energy transfer. Further, in the wolf-shaped scheme, circles represent planetary gear sets, and boxes represent non-planetary gear sets that may include shafts, gears, and the like. Each gear set may have an associated ratio. In addition, in the wolf-shaped scheme, the clutch is represented by parallel lines, and the joint portion where power is combined from the plurality of branch portions is represented by solid dots. The coupling portion may comprise a gear, a shaft section, etc. The transmission system 200 shown in FIG. 2 is an example of the transmission system 100 shown in FIG. 1. Due to this correspondence, these transmission systems may share common functional and structural features. And thus repetitive descriptions are omitted for the sake of brevity.

The transmission system 200 may include an internal combustion engine 202 or other suitable motive power source (e.g., an electric motor or a motor-generator). First junction 204 rotationally couples two

mechanical branches

206, 208 to a hydrostatic branch 210 having a hydrostatic assembly 212. The first mechanical branch 206 may be rotationally attached to a ring gear 214 in a first planetary gear set 216. Conversely, the second mechanical branch 208 may be rotationally attached to the carrier 218 in the second planetary gear set 220.

Hydrostatic assembly 212 includes a hydraulic pump 222 and a hydraulic motor 224. Further, a gear set 226 may be disposed in the hydrostatic branch between the pump 222 and the engine 202. The gear 226 may be rotationally coupled to a mechanical interface 227 of the pump 222. The hydraulic interface 228 in each of the pump and motor may be in fluid communication via a conduit 230. The mechanical interface 227 of the pump may be mechanically attached to the gear set 226. Further, the mechanical interface 234 of the motor may be mechanically attached to the second joint 236. The second junction 236 serves as a rotational connection between the sun gears 238, 240 of the first and second planetary gear sets 216, 220.

The transmission system 200 may also include a reverse clutch 242, a first forward clutch 244, and a second forward clutch 246. These clutches are mechanically coupled in parallel to allow one of the clutches to be engaged while the other clutch is disengaged in a different drive range. Thus, each clutch corresponds to a different drive range.

Gear set 248 may be rotationally coupled to carrier 250 of first planetary gear set 216. The gear set shown in fig. 2 may include two gears. Junction 252 may serve as a mechanical connection between gear set 248 and

clutches

242, 244. Additionally, gear set 254 may be rotationally coupled to reverse clutch 242, and gear set 256 is coupled to first forward clutch 244. Another junction 258 may be used to re-join mechanical branches associated with the reverse clutch and the first forward clutch. The ring gear 262 of the second planetary gear set 220 may be rotationally coupled to the gear set 260. Further, gear set 263 may be coupled to second forward clutch 246 and junction 264. The joint 264 may serve as the output of the three clutch branches.

Fig. 3-8 depict the power path through the transmission system 200 in different drive ranges. The cross-hatched arrows depict the circular power flow, wherein the power path travels back to the upstream component. In contrast, the non-cross-hatched arrows depict downstream power flow to the transmission output.

Turning specifically to FIG. 3, a transmission system operating in a first phase of a first drive range is shown. In the first drive range, the first forward drive clutch 244 is engaged and the reverse drive clutch 242 and the second forward drive clutch 246 are disengaged. Thus, in the first drive range, the transmission is in an input-coupled power-split mode.

In this power split mode, arrow 300 represents the power path from the engine 202 to the junction 204, from the junction 204 to the first mechanical branch 206, and from the first mechanical branch to the ring gear 214 of the first planetary gear set 216. Arrow 302 represents the recirculation of power from the sun gear 238 of the first planetary gear set 216 to the hydraulic motor 224, from the hydraulic motor to the hydraulic pump 222, from the hydraulic pump to the gear set 226, and from the gear set to the junction 204. Arrow 304 represents the power path from carrier 250 of first planetary gear set 216 to gear set 248, from gear set 248 via junction 252 to first forward drive clutch 244, from first forward drive clutch to gear set 256, and from gear set 256 to the output 306 of the transmission. In this way, a portion of the power is circulated back through the hydrostatic assembly 212, while another portion is transmitted through the clutch to the output. Due to the circulation of power through the hydrostatic assembly, the transmission may operate at relatively high efficiency compared to a mechanical or hydrostatic transmission alone.

In a second phase of the first drive gear range, the hydraulic power path changes direction. During this change of direction, the power in the hydraulic path crosses zero and enters the additional power of the mechanical and hydraulic paths, as shown in fig. 4.

In a second phase of the first drive range, the power path travels in parallel through the first mechanical branch 206 and the hydrostatic assembly 212. Further, in the second phase of the first drive range, power from the mechanical and hydrostatic branches is additively combined at the first planetary gear set 216 and then transmitted to the transmission output 306 through the first forward clutch 244. Specifically, as shown in fig. 4, arrow 400 represents the power path through the mechanical branch 206 to the ring gear 214 of the first planetary gear set 216. Further, arrow 402 represents the power path through the hydrostatic branch (gear set 226, hydraulic pump 222, and hydraulic motor 224) to the sun gear 238 of the first planetary gear set 216. Further, arrow 404 represents the power path from carrier 250 of first planetary gear set 216 to gear set 248, from gear set to first forward drive clutch 244, from first forward drive clutch to gear set 256, and from gear set to output 306.

When the ring gear speed of the second planetary gear set 220 allows synchronization of the second forward clutch 246, the drive range is changed (e.g., from the first drive range to the second drive range) by opening the first drive clutch 244 and closing the second drive clutch 246 via a synchro-shift. Closing a friction clutch involves the frictional engagement of multiple sets of plates in the clutch to transmit power between the input and output of the clutch. Conversely, opening a friction clutch involves frictional disengagement of the plates of the clutch to disengage the input and output of the clutch. Further, synchronizing the shift involves opening one clutch while closing the other clutch.

Fig. 5 accordingly illustrates the transmission system 200 operating in the first phase of the second forward drive range. In the second forward drive range, the transmission operates in a similar manner to the first forward drive range, but with a different mechanical path ratio. In the second range, the reverse clutch 242 and the first forward clutch 244 are each disengaged, while the second forward clutch 246 is engaged.

In the first phase, power is circulated back to second mechanical branch 208 through hydrostatic assembly 212. Arrow 500 specifically indicates the power path from the sun gear 240 of the second planetary gear set 220 to the hydrostatic assembly 212. Arrow 500 also indicates a power path through hydrostatic assembly 212 to gear set 226. The power path through the hydrostatic assembly involves power transmission through the hydraulic motor 224 and the hydraulic pump 222. The power path from the junction 204 through the second mechanical device branch 208 and to the carrier 218 of the second planetary gear set 220 is represented via arrow 502. Further, arrow 504 represents a power path from ring gear 262 to gear set 260, and through second forward clutch 246 and gear set 263 to output 306.

Fig. 6 shows the transmission system 200 operating in the second phase of the second forward drive range after the power flow in the hydraulic path has changed direction (switched from circulating power, zero power through the hydrostatic path, and transitioning to additional power flow to the mechanical and hydraulic branches). In this way, the ratio in the second forward drive range can be continuously adjusted across this range in an efficient manner.

Arrow 600 represents the power path from junction 204, through gearset 226 and hydrostatic assembly 212, to sun gear 240 of second planetary gearset 220. Arrow 602 represents the power path from the junction 204, through the second mechanical branch 208, and to the carrier 218 of the second planetary gear set 220. Additionally, arrow 604 represents a power path from the ring gear 262 of the second planetary gear set 220, through gear set 260, the second forward clutch 246, and gear set 263, and to the transmission output 306.

Fig. 7 and 8 show the first and second phases of the reverse drive range. The reverse range is similar to the first forward drive range, except that the output speed direction is reversed by the gear ratio in the mechanical path of gear set 254. In the reverse drive range, the reverse clutch is engaged while the first forward clutch and the second forward clutch are disengaged. Fig. 7 specifically depicts an arrow 700 that represents the power path from the junction 204, through the first mechanical branch 206, and to the ring gear 214 in the first planetary gear set 216. Arrow 702 represents the power path circulating through hydrostatic assembly 212 and gear set 226. Additionally, arrow 704 represents the power path from the ring gear 250 of the first planetary gear set 216, through gear set 248, reverse clutch 242, and gear set 254, and to the transmission output 306.

Also, during the reverse drive range, the power flow in the hydraulic path changes direction (switching from the power cycle configuration, zero power through the hydrostatic path, and transitioning to an additional power flow configuration, which is shown in FIG. 8). Arrow 800 in fig. 8 represents the power path that travels through the first mechanical branch 206 and to the ring gear 214 of the first planetary gear set 216. Arrow 802 represents the power path through the hydrostatic assembly 212 to the sun gear 238 of the first planetary gear set 216. After the power is additively combined in the first planetary gear set, the power travels from the carrier 250 to the output 306 via the reverse clutch 242, as shown via arrow 804.

Fig. 9 shows a chart 900 illustrating the configuration (engaged or disengaged) of the

clutches

242, 244, 246 shown in fig. 2-8 in different drive modes (reverse drive range, first forward drive range, and second forward drive range). In the reverse drive range, the reverse clutch 242 is engaged and the

clutches

244, 246 are disengaged. Additionally, in the first forward drive range, the first forward clutch 244 is engaged while the

clutches

242, 246 are disengaged, and in the second forward drive range, the second forward clutch 246 is engaged while the

clutches

242, 244 are disengaged. As previously described, the clutches may be shifted synchronously for smooth and efficient transitions between different drive modes.

Fig. 10 shows a graph 1000 in which the hydrostatic ratio is represented on the ordinate and the transmission ratio is represented on the abscissa. These ratios are examples of ratios that may be produced by the transmission systems described above with respect to fig. 1-9. In detail, the ordinate and abscissa indicate zero values of other respective ratios. Thus, the points below the abscissa represent negative hydrostatic ratios, while the points above the abscissa represent positive hydrostatic ratios. The points to the left of the ordinate represent negative gear ratios, while the points to the right of the ordinate represent positive gear ratios. Further, different drive ranges (reverse drive range, first forward drive range, and second forward drive range) for the transmission operating modes are divided. However, other transmission embodiments may have alternative correspondences between hydrostatic pressure ratios and transmission ratios.

In the reverse drive range, power is recirculated through the hydrostatic assembly in a first portion of the range. In contrast, in the second part of the range, power is additionally combined from the mechanical branch and the hydrostatic branch. The transmission ratio value-tr 1 represents the boundary between the first and second portions of the reverse drive range.

At 1002, a shift (e.g., a synchro-shift) occurs between the reverse clutch and the first forward clutch, and the transmission enters a first forward drive range, and vice versa. During a first portion of the drive range, power is recirculated through the hydrostatic assembly, similar to the reverse drive range. However, in the first forward drive range, the output of the transmission rotates in the opposite direction when compared to the reverse drive range. During a second portion of the first forward drive range, power from the hydrostatic assembly and the mechanical assembly is additionally combined at the first planetary gear assembly. The transmission ratio value tr1 represents the boundary between the first and second portions (recirculation and additional power arrangements) of the first forward drive range.

At 1004, a shift (e.g., a synchro-shift) occurs between the first forward clutch and the second forward clutch, and vice versa. During a first portion of the second forward drive range, power is recirculated from the second planetary gear set through the hydrostatic assembly. Conversely, in a second portion of the second forward drive range, power from the second mechanical branch and the hydrostatic assembly is additively combined at the second planetary gear set.

Fig. 11-12 show pump rotation angle diagrams with sequential control. These figures are used as examples of rotational angle adjustments that may be implemented via hydraulic pumps in the transmission system, as described above with respect to fig. 1-9. When using a fixed flex axis motor in the transmission, the rotational angle may be equal to the hydrostatic pressure ratio, which is shown in fig. 10. In detail,

graphs

1100, 1200 with pump rotation angle on the ordinate and hydrostatic pressure ratio on the abscissa are shown in fig. 11-12, respectively. The zero rotation angle and the hydrostatic pressure ratio are shown on both the ordinate and the abscissa. Although specific rotation angle and hydrostatic pressure ratios are not shown, negative and positive rotation angles (α) and ratios (r) are provided for reference only.

Fig. 11 shows the pump rotation angle for the forward drive mode. In the forward drive mode, the rotation angle of the pump reaches a maximum value (α 2) and then decreases as the hydrostatic ratio increases. On the other hand, fig. 12 shows the pump rotation angle in the reverse drive mode. In the reverse drive mode, as the pump rotation angle increases, the hydrostatic pressure ratio decreases until-r 1 is reached. Therefore, the pump rotation angle can be adjusted to change the ratio of the hydrostatic pressure branch portions in different drive modes.

FIG. 13 illustrates a method 1300 for operation of a hydromechanical transmission. In one example, the method 1300 may be performed by the hydromechanical transmission and components described above with respect to fig. 1-9. However, in other examples, method 1300 may be implemented using other suitable hydromechanical transmissions and corresponding components. Further, the method may be implemented as instructions stored in a non-transitory memory that are executed by a processor in the controller. Thus, performing the method steps may include sending and/or receiving a command that triggers the adjustment of the associated component, as previously described.

At 1302, the method includes determining an operating condition. The operating conditions may include transmission speed, transmission torque, vehicle speed, operator torque request, operator speed request, ambient temperature, transmission temperature, and the like. These operating conditions may be determined using sensor data and/or modeling algorithms.

At 1304, the method includes determining whether a torque or speed adjustment request has been received. For example, a torque or speed adjustment request may be generated in response to an operator interaction with an input device such as an accelerator pedal, a lever, a joystick, or the like.

If a torque or speed adjustment request has not been received ("NO" of 1304), the method proceeds to 1306, where the method includes maintaining a current transmission control strategy. For example, the transmission may be operated at a torque set point or, in some cases, a speed set point within one of the drive ranges.

If a torque or speed adjustment request has been received ("yes" at 1304), the method proceeds to 1308. At 1308, the method determines whether to change the drive mode. In detail, the transmission may be designed to implement two point synchronizations of the speed ratios of the two clutches. The first point synchronizes a first forward clutch (e.g., clutch 172 shown in fig. 1) and a second forward clutch (e.g., clutch 174 shown in fig. 1), while the second point synchronizes the first forward clutch and a reverse clutch (e.g., clutch 170 shown in fig. 1). The instructions in the controller of the transmission may be designed to control the torque provided by the transmission to the output shaft. Thus, the speed ratio of the transmission may be the result of the torque applied by the transmission. For example, if a higher tractive torque is applied to the output shaft through the transmission while the engine is operating at a substantially constant speed, a higher output shaft acceleration and therefore a higher speed ratio gradient occurs. The speed ratio of the transmission may change as a result of the operator torque adjustment request. At some point during acceleration, the speed ratio of the transmission will approach the maximum value possible within the current operating drive range. Thus, when the maximum speed value is approached, the operating drive range may be changed to prevent interruption of the traction torque continuity to the wheels. For example, the transmission may transition from a reverse drive range to a first forward drive range, or from the first forward drive range to a second forward drive range. Conversely, the transmission may also change the operating drive range when the actual speed ratio of the transmission is near the minimum of the operating drive range. For example, the transmission may transition from the second forward drive range to the first forward drive range, or from the first forward drive range to the reverse drive range. Thus, in such an example, a mode change operation may be implemented in which the transmission is transitioned from a first forward drive range (e.g., a synchronous transition) to a second forward drive range. However, if the torque or speed adjustment request can be processed within the current operational drive range, the drive mode change can be temporarily suppressed.

If it is determined that a mode change should not be performed ("NO" of 1308), the method moves to 1310. At 1310, the method includes operating the transmission in one of the drive ranges to adjust a transmission output torque. For example, the hydrostatic assembly may be adjusted to change the output torque of the transmission in one example or to change the speed in another example.

Operating the transmission in one of the drive ranges may include either 1312 or 1314, or transitioning between

blocks

1312 and 1314, or vice versa. At 1312, the method may include additively combining power from one of the mechanical components and the mechanical branch in the hydrostatic component through one of the planetary gear sets. In this way, power may be efficiently combined in the transmission to achieve a target speed or torque.

At 1314, the method may include recirculating power through the hydrostatic assembly while transferring a portion of the power from one of the mechanical branches in the mechanical assembly through one of the planetary gear sets to the transmission output.

However, if it is determined that a mode change request should be performed ("yes" at 1308), the method proceeds to 1316. In one example, a shift command may be generated (e.g., automatically generated) when it is determined that a mode change request should be implemented. Thus, the shift request may be a request to shift between the reverse drive range and the first forward drive range, or between the first forward drive range and the second forward drive range, or vice versa. At 1316, the method includes transitioning between two of the drive ranges. This transition, which may be referred to as a shift transient, may include step 1318. At 1318, the method includes synchronizing operation of the two clutches to transition between the two drive ranges. For example, the reverse clutch may be disengaged while the first forward clutch is engaged, and vice versa. In another example, the first forward clutch may be disengaged while the second forward clutch is engaged while the output shaft torque remains at a desired value, and vice versa. In this way, the transmission operating drive range can be changed to prevent interruption of tractive torque continuity to the wheels. Thus, transmission performance is improved, thereby improving customer satisfaction. It should be appreciated that the transmission drive mode transition may be performed automatically. That is, the drive modes may be switched based on the speed ratio of the transmission rather than explicitly requesting a switch between drive modes via operator interaction with the gear selector.

Method 1300 allows transmission torque adjustment to be performed smoothly and efficiently. As a result, in some cases, the operating efficiency of a vehicle using the transmission is improved and the transmission life may be increased accordingly. Thus, method 1300 can enhance transmission performance.

Fig. 14 illustrates a predicted use case power limit curve 1400. The power limiting curve may correspond to one example embodiment of the hydromechanical transmission previously described. Torque is shown on the ordinate and speed on the abscissa. In detail, the ordinate is the zero speed value, while the abscissa is the zero torque value. Thus, the negative velocity value is located to the left of the ordinate, while the positive velocity value is located to the right of the ordinate. Furthermore, the positive torque values are located above the abscissa, while the negative torque values are located below the abscissa.

As shown in fig. 14, the maximum torque in the first forward drive range may be greater than the maximum torque in the reverse drive range. Further, the maximum speed in the reverse drive range may be-2000 RPM, while the maximum speed in the second forward drive range may be 3700RPM. In this way, the maximum output speed of the transmission may be asymmetric for the forward and reverse directions. However, many suitable maximum torque and speed values have been envisaged. The power limiting curve of the transmission may be selected based on end use vehicle design parameters such as vehicle weight, expected PTO load, expected vehicle load, etc.

In another predictive use case embodiment, the transmission may provide 100% tractive effort at 1500RPM and 40% tractive effort at 900 RPM. This may allow the transmission to meet a range of loads that the transmission may be expected to experience in several intended operating environments. However, other transmission embodiments may have tractive effort mapped to different speeds, and this correlation may be set based on a variety of factors such as expected transmission load, transmission operating efficiency, and the like.

FIG. 15 shows a predicted use case plot 1500 of transmission speed versus time and a plot 1502 of transmission tractive torque versus time. Thus, for

curves

1500, 1502, the speed ratio and tractive torque are on the ordinate, while time is on the abscissa. The tractive torque may be a controlled variable. As previously described, a drive range transition may be initiated when the speed ratio of the transmission approaches the threshold r1. The threshold r1 may specifically correspond to the maximum value possible within the current driving range. Thus, the transmission may transition between the first drive range and the second drive range when the maximum value is approached. However, in other examples, the threshold may correspond to the minimum possible within the current driving range as the speed ratio decreases. Thus, in such an example, the transmission may transition from the second drive range to the first drive range, or from the first drive range to the reverse drive range, when the minimum speed ratio is reached. Returning to the example depicted in FIG. 15, the first forward drive clutch may be synchronized with the second forward drive clutch when transitioning from the first drive range to the second drive range. Synchronization of the clutches may include decreasing torque transfer through the first forward clutch while correspondingly increasing torque transfer through the second forward clutch to maintain a desired transmission output torque.

FIG. 16 shows predicted use case curves 1600, 1602 for clutch differential speed versus time. Thus, on the ordinate, the clutch differential speed is present, and on the abscissa, the time is present. Curve 1600 specifically corresponds to the differential speed for the first forward drive clutch, and curve 1602 corresponds to the differential speed for the second forward drive clutch. FIG. 16 also shows predicted use case curves 1604, 1606 for clutch pressure versus time. Thus, on the ordinate, the clutch pressure is plotted, and on the abscissa, the time is plotted. Curve 1604 specifically corresponds to the first forward drive clutch, while curve 1606 corresponds to the second forward drive clutch. As shown, the differential speed of the first forward drive clutch remains zero until t1, after which it increases. Conversely, the differential speed of the second forward drive clutch is reduced until it reaches zero at t1, after which the differential speed remains zero. Accordingly, the pressure delivered to the first forward clutch is reduced until t1, and the pressure delivered to the second forward clutch is adjusted to cause the clutches to engage. For example, the pressure delivered to the second forward drive clutch may be adjusted to move the clutch through a fill phase and into a clutch trim phase, where the clutch moves toward full engagement.

The sum of the torque transferred by each of the two clutches involved in the shift (e.g., the first forward drive clutch and the second forward drive clutch in the illustrated example) allows the transmission to maintain a desired output shaft torque. In this way, transmission performance may be enhanced via a reduction in torque interruption that occurs during shift transients as compared to certain prior types of multi-speed transmissions.

Fig. 17 shows a predicted use-case curve 1700 for hydrostatic motor torque versus time. Thus, hydrostatic motor torque is on the ordinate and time is on the abscissa. FIG. 17 also shows predicted use case curves 1702, 1704 for clutch pressure versus time. Thus, on the ordinate, the clutch pressure is plotted, and on the abscissa, the time is plotted. Curve 1702 corresponds specifically to the pressure for the first forward clutch, while curve 1704 corresponds to the pressure for the second forward clutch. As shown, in fig. 17, the hydrostatic motor torque decreases below a zero value during the transition from the first drive mode to the second drive mode. In detail, the hydrostatic motor torque set point may be calculated based on the amount of torque transferred through the two clutches involved in the drive mode transition. Determining the hydrostatic motor torque set point in this manner enables the engaging second forward clutch to be synchronized with the first forward drive clutch. Further, during a shift event, the hydrostatic unit may be a "slave" to the clutch. In other words, during a shift, the hydrostatic unit may be controlled based on the engagement and disengagement of the clutch during the shift.

Fig. 18 shows the transmission system 100 operating to shift into a reverse gear. In detail, the torques of the hydraulic motor 134, the reverse clutch 170, the first forward drive clutch 172, and the output shaft 171 in the hydrostatic assembly 130 are represented by

arrows

1800, 1802, 1804, 1806, respectively. During a reverse shift operation, the hydrostatic motor torque may work in the same direction as the torque of the clutch to enable synchronization of the oncoming clutch (i.e., the clutch that begins transitioning to the fully engaged configuration). Equation (1) may thus represent a relationship between motor and clutch torques, where a and b are mechanical gains, C1 torque is the torque of the first forward drive clutch, and C2 torque is the torque of the second forward drive clutch.

Motor torque = a (C1 torque) + b (C2 torque) (1)

Further, the clutch may enable a desired torque to be applied to the output shaft. Equation (2) may represent a relationship between the output torque and the respective clutch torques, where the output torque is the torque of the output shaft, C and d are mechanical gains, the C1 torque is the torque of the first forward drive clutch, and the C2 torque is the torque of the second forward drive clutch.

Output torque = C (C1 torque) + d (C2 torque) (2)

Synchronizing the clutches in this manner allows torque interruptions to be substantially avoided during shift transients, if desired. Therefore, the shifting performance can be enhanced and the efficiency of the transmission can be improved.

A technical effect of the hydromechanical transmission and transmission operating methods described herein is to provide a target set of drive ranges in an energy and space efficient package. Further, the transmission systems and methods described herein allow the transmission to transition smoothly between different drive ranges with a reduced amount of power interruption (e.g., substantially zero), thereby reducing NVH during mode shift transients and further improving transmission energy efficiency.

Fig. 1-8 and 18 show example configurations with relative positioning of various components. Such elements, at least in one example, may be referred to as being in direct contact or directly coupled, respectively, if shown as being in direct contact or directly coupled to each other. Similarly, elements shown as being continuous or adjacent to one another may be continuous or adjacent to one another, respectively, at least in one example. By way of example, components placed in face-sharing contact with each other may be referred to as face-sharing contact. As another example, in at least one example, elements that are positioned spaced apart from one another with only a spacing space therebetween and no other components may be so called. As yet another example, elements shown above/below each other, on opposite sides of each other, or left/right of each other may be so called with respect to each other. Further, as shown in the figures, in at least one example, a topmost element or point of elements may be referred to as a "top" of a component, while a bottommost element or point of elements may be referred to as a "bottom" of the component. As used herein, top/bottom, upper/lower, above/below may be with respect to a vertical axis of the drawings and are used to describe the positioning of elements of the drawings with respect to each other. Thus, in one example, an element shown above another element is positioned vertically above the other element. As yet another example, the shapes of elements depicted in the figures may be referred to as having such shapes (e.g., such as rounded, rectilinear, planar, curved, rounded, chamfered, angled, etc.). Further, in one example, elements that are coaxial with each other may be referred to as such. Further, in at least one example, elements shown as intersecting one another may be referred to as intersecting elements or intersecting one another. Further, in one example, an element shown as being within another element or external to another element may be referred to as such. In other examples, elements that are offset from each other may be referred to as such.

The invention will be further described in the following paragraphs. In one aspect, a transmission system is provided that includes a hydraulic pump and a hydraulic motor rotationally coupled in parallel with a first planetary gear set and a second planetary gear set; wherein the sun gears of the first and second planetary gear sets are rotationally coupled to the hydraulic motor; and wherein the carrier of the first planetary gear set is rotationally coupled to the first clutch and the second clutch; and wherein the ring gear of the second planetary gear set is rotationally coupled to the third clutch.

In another aspect, a hydromechanical variable transmission is provided, the transmission including a hydraulic pump and a hydraulic motor rotationally coupled in parallel with a first planetary gear set and a second planetary gear set; wherein the sun gears of the first and second planetary gear sets are rotationally coupled to the hydraulic motor; and wherein the carrier of the first planetary gear set is rotationally coupled to the first forward clutch and the reverse clutch; and wherein the ring gear of the second planetary gear set is rotationally coupled to the second forward clutch.

In another aspect, a power splitting transmission is provided, the transmission including a hydraulic pump and a hydraulic motor rotationally coupled in parallel with a first planetary gear set and a second planetary gear set; wherein the sun gears of the first and second planetary gear sets are rotationally coupled to the hydraulic motor; and wherein the carrier of the first planetary gear set is rotationally coupled to the first forward clutch and the reverse clutch; and wherein the ring gear of the second planetary gear set is rotationally coupled to the second forward clutch.

In yet another aspect, a transmission system is provided that includes a hydrostatic assembly and a mechanical assembly coupled in parallel via a first planetary gear set and a second planetary gear set; a plurality of clutches coupled in parallel to a transmission output, comprising:

a first clutch rotationally coupled to a carrier of the first planetary gear set; a second clutch rotationally coupled to the carrier in parallel with the first clutch; and a third clutch rotationally coupled to the ring gear of the second planetary gear set; a controller comprising instructions stored in a non-transitory memory that, when executed by the processor, in response to receiving a speed or torque change request, cause the controller to: the first clutch, the second clutch, and/or the third clutch are operated to transition between two drive ranges in a set of drive ranges, wherein the set of drive ranges includes at least one reverse drive range and two forward drive ranges.

In another aspect, a method for operating a transmission system includes transitioning between engaged and disengaged states of one or more of a reverse clutch, a first forward clutch, and a second forward clutch when switching between two drive modes of a group drive mode; wherein the first forward clutch is coupled to the carrier of the first planetary gear set, the reverse clutch is coupled to the carrier in parallel with the first forward clutch, and the second forward clutch is coupled to the ring gear of the second planetary gear set; and wherein the hydrostatic assembly, the first mechanical branch and the second mechanical branch are coupled to the first planetary gear set and the second planetary gear set in parallel. In one example, the method may further include operating the transmission system in one of the drive modes, and delivering power from the first planetary gear set or the second planetary gear set to a mechanical component of the transmission system while operating in one of the drive modes, wherein the mechanical component is arranged in parallel with the hydrostatic component.

In yet another aspect, a hydromechanical variable transmission is provided, the transmission including a hydrostatic assembly and a mechanical assembly coupled in parallel via a first planetary gear set and a second planetary gear set; a plurality of clutches coupled in parallel to a transmission output, comprising: a first clutch coupled to a carrier of the first planetary gear set; a second clutch coupled to the carrier in parallel with the first clutch; and a third clutch coupled to the ring gear of the second planetary gear set; and a controller including instructions stored in a non-transitory memory executable by the processor, the instructions causing the controller to, during a shift transient: operating the first clutch, the second clutch, and/or the third clutch to transition between two drive ranges in the set of drive ranges; wherein the set of drive ranges includes at least one reverse drive range and two forward drive ranges.

In any aspect or combination of aspects, the second clutch may be a reverse clutch.

In any aspect or combination of aspects, the first clutch and the reverse clutch may each be directly coupled to the carrier and adjacent to each other.

In any aspect or combination of aspects, the first clutch, the second clutch, and the third clutch may be friction clutches.

In any aspect or combination of aspects, the transmission system may further include a mechanical power take-off (PTO) rotationally coupled to a mechanical branch extending between the power source and the hydraulic pump.

In any aspect or combination of aspects, the transmission system may further include a mechanical power take-off (PTO) coupled to the hydraulic pump.

In any aspect or combination of aspects, the hydraulic motor may be a fixed bent axis motor.

In any aspect or combination of aspects, the hydraulic pump can be an axial piston pump.

In any aspect or combination of aspects, the first planetary gear set and the second planetary gear set may be coaxially arranged.

In any aspect or combination of aspects, the first clutch and the second clutch may be axially offset from the third clutch.

In any aspect or combination of aspects, the transmission system may be included in an off-highway vehicle.

In any aspect or combination of aspects, the transmission system may further include an input interface configured to be rotationally coupled to the motive power source and an output interface configured to be rotationally coupled to one or more axles, and wherein the input interface is axially offset from the output interface.

In any aspect or combination of aspects, the hydromechanical variable transmission may be a continuously variable transmission.

In any aspect or combination of aspects, the hydromechanical variable transmission may include a mechanical power take-off (PTO) coupled to an input shaft that receives rotational input from a motive power source. In any aspect or combination of aspects, the first forward clutch and the reverse clutch may be disposed coaxially with each other and axially offset from the second forward clutch and the first and second planetary gear sets.

In any aspect or combination of aspects, the hydraulic motor may be a fixed bent-axis motor, and wherein the hydraulic pump is a variable displacement axial piston pump.

In any aspect or combination of aspects, the first forward clutch, the reverse clutch, and the second forward clutch may be coupled in parallel with each other.

In any aspect or combination of aspects, the first forward clutch and the reverse clutch may be coupled to a first central shaft that is radially offset from a second central shaft coupled to the second forward clutch.

In any aspect or combination of aspects, the transmission system can further include instructions stored in the non-transitory memory that, when executed by the processor, cause the controller to: the hydrostatic assembly and the mechanical assembly are operated to additionally deliver power to the first planetary gearset or the second planetary gearset.

In any aspect or combination of aspects, the transmission system may further include instructions stored in the non-transitory memory that, when executed by the processor, cause the controller to: the hydrostatic assembly is operated to circulate power from the first planetary gear set or the second planetary gear set back to the mechanical assembly.

In any aspect or combination of aspects, operating the first clutch, the second clutch, and the third clutch to shift between the two drive ranges may include: when the ring gear in the second planetary gear set allows synchronization of the third clutch, the second clutch is opened and the third clutch is closed.

In any aspect or combination of aspects, the second clutch may be a reverse drive clutch, and the first clutch and the third clutch are forward drive clutches.

In any aspect or combination of aspects, the transition between the two drive ranges may be implemented synchronously.

In any aspect or combination of aspects, the set of drive ranges may include only the reverse drive range and the two forward drive ranges.

In any aspect or combination of aspects, transitioning between engaged and disengaged states of one or more of the reverse clutch, the first forward clutch, and the second forward clutch can include: when the ring gear in the second planetary gear set allows synchronization of the second forward clutch, the first forward clutch is opened and the second forward clutch is closed.

In any aspect or combination of aspects, a transition between the two drive modes may be initiated in response to a torque modulation request, and wherein the carrier drive mode includes a reverse drive range, a first forward drive range, and a second forward drive range.

In any aspect or combination of aspects, operating the transmission system in one of the drive modes may comprise: the hydrostatic assembly is operated in a portion of the drive range to deliver power to the first planetary gear set or the second planetary gear set in additional combination with one of the first mechanical branch and the second mechanical branch.

In any aspect or combination of aspects, operating the transmission system in one of the drive modes may include: power is transmitted through only one of the reverse clutch, the first forward clutch, and the second forward clutch.

In any aspect or combination of aspects, operating the first clutch, the second clutch, and/or the third clutch to transition between the two drive ranges may include: simultaneously with opening one of the first clutch, the second clutch, and the third clutch, closing another one of the first clutch, the second clutch, and the third clutch.

In any aspect or combination of aspects, when the ring gear in the second planetary gear set allows synchronization of the synchronously opened and closed clutches, opening one of the first clutch, the second clutch, and the third clutch and closing another one of the first clutch, the second clutch, and the third clutch may be achieved.

In any aspect or combination of aspects, the hydromechanical variable transmission may further include instructions stored in the non-transitory memory that, when the hydromechanical variable transmission is operating in one of the two forward drive ranges or a first portion of the reverse drive range, when executed by the processor, cause the controller to: operating the hydrostatic assembly to deliver power from the first planetary gearset or the second planetary gearset to the mechanical assembly; and instructions stored in the non-transitory memory that, when executed by the processor, cause the controller to: the hydrostatic and mechanical assemblies are operated to additionally deliver power to the first or second planetary gear sets.

In any aspect or combination of aspects, power flow may circulate from one of the first planetary gear set and the second planetary gear set to the hydrostatic assembly and from the hydrostatic assembly to the input of the mechanical assembly in a portion of each of the reverse drive range and the two forward drive ranges.

In any aspect or combination of aspects, power flow from the hydrostatic assembly and the mechanical assembly may pass through an additional combination of the first and second planetary gear sets in a portion of each of the reverse drive range and the two forward drive ranges.

In any aspect or combination of aspects, the mechanical PTO may be coupled with an input interface that receives rotational input from a motive power source (e.g., a prime mover).

In any aspect or combination of aspects, the set of drive ranges may include at least one reverse drive range and two forward drive ranges.

In another expression, an off-highway vehicle is provided having a hydrostatic mechanically variable transmission including synchronous forward and reverse clutches rotationally coupled in parallel with each other and in series with a mechanical branch and a hydrostatic branch. Further, in the transmission, the hydrostatic branch and the mechanical branch are rotationally coupled in parallel.

In another expression, a method for transitioning between operating drive ranges in a hydrostatic mechanically variable transmission is provided. The method includes synchronously closing the forward clutch while opening the reverse clutch during a mode change transient. The transmission further comprises a hydraulic branch arranged to be rotationally attached in parallel to the mechanical branch, and both the hydraulic branch and the mechanical branch are rotationally attached to a pair of planetary gear sets positioned coaxially with respect to each other.

While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to those skilled in the relevant art that the disclosed subject matter can be embodied in other specific forms without departing from the spirit of the subject matter. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

It is noted that the example control and estimation routines included herein may be used with various powertrain and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in a non-transitory memory and may be executed by a control system including a controller in combination with various sensors, actuators, and other or vehicle hardware. Furthermore, several parts of the method may be physical actions taken in the real world to change the state of the device. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various acts, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing to achieve the features and advantages of the example examples described herein is not essential, but is provided for ease of illustration and description. One or more of the illustrated acts, operations, and/or functions may be repeatedly performed depending on the particular strategy being used. Further, the described acts, operations, and/or functions may graphically represent code to be programmed into the non-transitory memory of the computer readable storage medium in the vehicle and/or transmission control system, with the described acts being performed by executing instructions in a system comprising the various hardware components and in conjunction with the electronic controller. One or more of the method steps described herein may be omitted, if desired.

It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific examples are not to be considered in a limiting sense, because numerous variations are possible. For example, the above techniques may be applied to powertrains that include different types of propulsion sources, including different types of electric machines, internal combustion engines, and/or transmissions. The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. These claims may refer to "an" element or "a first" element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.

As used herein, the terms "about" and "substantially" are to be construed as meaning plus or minus five percent of the range, unless otherwise indicated.

Claims

1. A transmission system comprising:

a hydraulic pump and a hydraulic motor rotationally coupled in parallel with the first and second planetary gear sets;

wherein the sun gears of the first and second planetary gear sets are rotationally coupled to the hydraulic motor; and is provided with

Wherein a carrier of the first planetary gear set is rotationally coupled to a first clutch and a second clutch; and is

Wherein the ring gear of the second planetary gear set is rotationally coupled to the third clutch.

2. The transmission system of claim 1, wherein the second clutch is a reverse clutch.

3. The transmission system of claim 2, wherein the first clutch and the reverse clutch are each directly coupled to the carrier and are adjacent to each other.

4. A transmission system as recited in claim 1, wherein the first clutch, the second clutch, and the third clutch are friction clutches.

5. The transmission system of claim 1, further comprising a mechanical power take-off (PTO) rotationally coupled to a mechanical branch extending between a power source and the hydraulic pump.

6. The transmission system of claim 1, further comprising a mechanical Power Take Off (PTO) coupled to the hydraulic pump.

7. The transmission system of claim 1, wherein the hydraulic motor is a fixed bent axis motor.

8. The transmission system of claim 1, wherein the hydraulic pump is an axial piston pump.

9. The transmission system of claim 1, wherein the first planetary gear set and the second planetary gear set are coaxially arranged.

10. A transmission system as recited in claim 1, wherein the first clutch and the second clutch are axially offset from the third clutch.

11. A transmission system as claimed in claim 1, characterised in that the transmission system is included in an off-highway vehicle.

12. The transmission system of claim 1, further comprising an input interface configured to be rotationally coupled to a motive power source and an output interface configured to be rotationally coupled to one or more axles, and wherein the input interface is axially offset from the output interface.

13. The transmission system of claim 1, wherein the transmission system is a continuously variable transmission.

14. The transmission system of claim 1, wherein the hydraulic motor is a fixed bent-axis motor, and wherein the hydraulic pump is a variable displacement axial piston pump.

15. A transmission system as recited in claim 1, wherein said first clutch, said second clutch, and said third clutch are coupled in parallel with one another.